I'm also having a problem with updating my X-T100 firmware. I format the SD card on my camera, put the card in my PC running WIN10, download the firmware from the Fuji site and see the two files (FWUP0023.DAT for the camera and XFUP0029.zip for the lens). I've also tried doing this just for the camera.
Then I insert my SD card into the PC and put those files on the card and put the card in my camera. When I turn on the camera holding the DISP/BACK button, I see the same versions that came with the camera. When I click on OK I get a screen that says Select Item. When I select lens or camera, in each case I get a message "New firmware not be found. Turn off camera."
I have repeated this process several times to no avail. Suggestions?